(1) Field of the Invention
The present invention generally relates to a touch panel (an input device), and more particularly to a touch panel having a structure in which an input panel outputting signals corresponding to positions at which a pen or a finger presses on the input panel is on a display panel, such as an LCD (liquid crystal display) panel, having display elements arranged in a lattice.
(2) Description of the Related Art
A conventional touch panel (input device) of this type has a structure as shown in FIGS. 1A, 1B and 1C.
FIG. 1A shows a cross-sectional view of the touch panel. Referring to FIG. 1A, the touch panel has a structure in which an input panel 20 is on a display surface of a liquid crystal display (hereinafter referred to as an LCD) panel 10. The input panel outputs signals corresponding to positions at which a pen or a finger presses. The input panel 20 has transparent resistive films 21 and 22, a glass substrate 23 and a protection film 24. A plurality of dot spacers 30 are interposed between the transparent resistive films 21 and 22 so that the transparent resistive films 21 and 22 are maintained at a predetermined distance. Each of the dot spacers 30 is made of an insulating material. The transparent resistive film 22 is fixed on the glass substrate 23, and a top surface of the transparent resistive film 21 is covered by the protection film 24.
When a pen or a finger presses at a position on the protection film 24 of the input panel 20, the transparent resistive films 21 and 22 are brought into contact with each other at the position. The position at which the transparent resistive films 21 and 22 are in contact with each other is electrically detected.
A distance between each two of the dot spacers 30 two-dimensionally arranged affects a load (an input load) by which a pressing position on the input panel 20 can be detected. Thus, in order that input operations can be smoothly performed with a constant load all over the input panel 20, it is preferable that the dot spacers 30 should be two-dimensionally arranged at constant intervals. Thus, the dot spacers 30 are generally on lattice points of a lattice having a lattice distance d1 as shown in FIG. 1B. The lattice distance d1 is decided so that input operations can be performed with a predetermined input load.
In addition, as shown in FIG. 1C, display elements (display dots) 15 are on lattice points of a lattice having a lattice distance d2 on a display surface of the LCD panel 10.
Conventionally, a relationship between a first lattice in which the display dots 15 of the LCD panel 10 are arranged and a second lattice in which the dot spacers 30 in the input panel 20 are arranged has been not studied. In general, the input panel 20 is set on the LCD panel 10 such that two-dimensional directions (A21, A22) in which the display dots 15 of the LCD panel 10 are arranged in the first lattice are respectively equal to two-dimensional directions (A11, A12) in which the dot spacers 30 in the input panel 20 are arranged in the second lattice.
In the touch panel having the conventional structure described above, moire fringes may appear on the input panel 20. This may be caused by overlapping two types of lattices with each other. That is, interference of the display dots 15 arranged in the first lattice with the dot spacers 30 arranged in the second lattice may cause moire fringes on the input panel 20. The moire fringes on the input panel 20 deteriorates the display quality.